Contact units that are used in contact probes for electrically testing conductive patterns of printed circuit boards and electronic devices include those having a pair of needle members that are disposed so as to be moveable in the axial direction on either axial end as disclosed in Japanese UM laid open publication No. 60-154868. Such an electroconductive contact unit having two moveable ends is typically used for temporarily connecting, for testing purposes, two circuit boards that are eventually permanently connected in the final product. LCD panels and array circuit boards can be tested by using a contact probe having a same number of contact units as the number of electrodes in the circuit pattern of the LCD panel. The testing of the LCD panel typically takes place before the LCD panel is finally connected to a TAB consisting of a panel drive LSI and a printed circuit board.
As disclosed in Japanese patent application No. 06-87337 by the same applicant, an electroconductive contact probe holder can be formed by laminating a plurality of insulating plastic plates one over another. In each contact unit of such a contact probe, electroconductive needle members are provided on either end of a compression coil spring, and a holder hole for receiving this assembly is formed by a hole passed across the thickness of these insulating plates.
A specific example is illustrated in FIG. 9, small diameter holes 41a, 41b, 42a and 42b are formed in upper and lower insulating members 41 and 42, and large diameter holes 43a and 43b are formed in intermediate insulating members 43 laminated between the upper and lower insulating members 41 and 42 so that coil springs 44 and 45 are received in the corresponding large diameter holes 43a and 43b and the needle portions of the needle members 46, 47, 48 and 49 are supported by the corresponding small diameter holes 41a, 41b, 42a and 42b. Each needle member 46-49 is provided with a flange portion adapted to be received in the corresponding large diameter hole 43a or 43b and engage a shoulder defined between the corresponding large diameter hole 43a or 43b and small diameter hole 41a, 41b, 42a or 42b to prevent the corresponding needle member 46-49 from coming off.
These insulating members 41 to 43 jointly form a laminated assembly 50, and a plurality of contact units 51 each comprising a coil spring 44 and a pair of needle members 46 and 48 are arranged in this holder, the number of the contact units 51 corresponding to the number of the terminals of an LCD panel 53. The insulating members 41 to 43 may be joined to each other by using threaded bolts or a bonding agent. In the illustrated example, each contact unit 51 is electrically connected to another contact unit 52 consisting of a coil spring 45 and needle members 47 and 49 via a sheet portion 54a of a TAB 54 provided on the upper surface of the upper insulating member 41, and the needle member 49 of the contact unit 52 is in turn connected to an external testing device via a PCB 55 provided on the lower surface of the lower insulating member 42.
The holder 50 for the contact units each having two moveable ends is constructed as described above, and includes holder holes consisting of large diameter holes 43a and 43b and small diameter holes 41a, 41b, 42a and 42b. An arm 56 of an actuator supports the holder 50 via a part of the intermediate insulating member 43, for instance. In the course of a test, the arm 56 is moved and the needle members 48 are resiliently engaged with the terminals of the LCD panel 53.
However, according to this arrangement, because each of the insulating members that form the holder consists of a single piece member made of plastic material, dimensional errors may be produced in the holder over time owing to the change in temperature during the test (test under a high temperature condition), residual stress produced by a machining or other working process and absorption of moisture. Such dimensional errors give rise to changes in the pitch between adjacent holder holes and the positional precision of the contact point of each contact unit (the position of the tip of the needle member) may be impaired.